The invention relates to a straightener for straightening a metal strip and/or flat metal parts. Accordingly, a straightener of the present type comprises a number of upper straightening rolls which are mounted in an upper roll frame and a number of lower straightening rolls which are mounted in a lower roll frame. The roll frames are connected to one another by a plurality of stay bolts, the stay bolts being attached to the roll frames in such a way that the roll frames are held at a preselectable spacing from one another. This makes it possible that a straightening gap which is formed between the upper and lower straightening rolls can be changed, in order for it to be possible to straighten material of different thickness in the straightener.
Straighteners of the present type serve to eliminate stresses and unevennesses in metal strips or metal parts. The upper and lower straightening rolls are arranged offset with respect to one another, with the result that the material to be straightened is guided through the straightening rolls in a type of sinuous line, that is to say is bent alternately upward and downward. The bending takes place in such a way that the material is bent beyond its yield point at least at the first straightening rolls, with the result that undesired bending and stresses are eliminated in the material as completely as possible. The material is usually plasticized to a very pronounced extent at the first straightening roll of the straightener. The material is bent to a somewhat lesser extent at every further straightening roll, and the material is no longer plasticized at the last straightening roll, that is to say is only deformed elastically.
In the metal-processing industry, metal strips are often used which are supplied as what are known as coils and are unwound therefrom for production purposes. As a result of the winding up of the strip material to form coils, but also as a result of any possible previous thermal treatments and the like, there are unevennesses and stresses in the strip material which are unfavorable for further processing. After being unwound from the coil, metal strips are therefore as a rule guided through a straightener of the present type which they leave in a flat and stress-free state.
However, this is not the only field of application, since flat metal parts which are to be freed from undesired bends and stresses, are also as a rule straightened in a straightener of the present type, in order for it to be possible to process them further. Here, in particular, the adjustability of the straightening gap in a straightener of the present type is utilized particularly advantageously, since the parts to be straightened often have a different thickness or have to be treated with different bending moments. In both cases, it is then necessary to adapt the straightening gap correspondingly.
If a metal strip or a flat metal part is moved through the straightening gap and is bent alternately around the upper and lower straightening rolls, very high opposing forces are naturally produced in the straightener, which opposing forces are directed at opening or widening the straightening gap. The roll frames and, in particular, the stay bolts which hold the roll frames in the desired position with respect to one another therefore have to be of correspondingly robust design. The stay bolts are subject to a tensile load by the opposing forces during straightening, which is rendered perceivable by an elongation of the stay bolts in the case of corresponding forces.
A known option for dealing with said problem comprises in configuring the stay bolts to be correspondingly robust, that is to say very solid. This entails the disadvantage that the straightener becomes very heavy overall and is correspondingly expensive to manufacture as a result of the required material.
Another option for avoiding the widening of the straightening gap during operation is to compensate for the elongation of the stay bolts, by their effective length being shortened, that is to say by counteracting the elongation. As long as strip material is being straightened, this can be brought about very simply by the fact that the stay bolts which are connected as a rule by means of threads to the roll frames are tightened and their effective length is thus shortened to such an extent that the straightening gap obtains the desired extent again. This is because, if the strip material has run into the straightener once and the stay bolts have been correspondingly lengthened, one-time readjustment of the effective length of said stay bolts is sufficient, in order to produce defined conditions for the rest of the coil.
However, this is different in the case of part straighteners, since, in the case of every flat metal part which runs into the straightener, the latter rears up, that is to say the stay bolts are lengthened and the straightening gap yields or opens, which cannot be compensated for by simple readjustment of the stay bolt mounting brackets. This is because the straightening gap would then narrow excessively when a straightened part leaves the straightener, with the result that the next part to be straightened cannot run correctly into the straightener.
In order to solve this problem, it has been proposed in the prior art to provide the stay bolts with adjusting apparatuses in order to change their effective length, with the result that changes in the effective length of the stay bolts during operation, as a rule elongations, can be compensated for depending on measured results of a sensor for detecting the straightening gap in real time. An example for this is found in EP-A-1 673 181.
Since high forces act on the stay bolts during the straightening, and forces which are likewise correspondingly high are required to compensate for an increase in the effective length of said stay bolts, the adjusting apparatuses which are proposed in the prior art are equipped with hydraulic piston/cylinder units. The latter can generate and maintain the required forces in the required short reaction time. It is disadvantageous here, however, that a straightener which is equipped with adjusting apparatuses of this type has to be provided with an additional hydraulic system. Hydraulic systems which are not necessary in the case of a straightener without adjusting apparatuses are structurally complicated, however, and are intensive in terms of energy and maintenance. Moreover, their long-term service life leaves a lot to be desired in comparison with the other parts of a straightener of the present type, insofar as oil losses cannot be tolerated.